The present invention is directed to one aspect of the molding process used to mold multi-fiber optical fiber ferrules of the type described in U.S. Pat. No. 5,214,730 to Nagasawa et al. The reference numerals 2, 3, 4 and 6 used in the Background of the Invention section are the same as those used in the Nasasawa patent. The multi-fiber ferrule is generally indicated by reference numeral 3 in FIG. 1 of Nagasawa. The term ferrule is used herein instead of the term "plug assembly" used in Nagasawa. "Ferrule" is a term of art that refers to the structure that receives the end of an optical fiber or fibers and then is abutted against an opposing ferrule to precisely align optical fibers for transmission of an optical signal. With reference to FIG. 1 of Nagasawa, the multi-fiber ferrule includes an array of optical fibers 2 disposed therein and guide bores 4 for receiving guide pins 6 to align two ferrules during the mating of the two ferrules.
In the typical molding of ferrules 3, bore forming pins extend through the mold cavity to create the guide bores 4 and the bores that receive optical fibers 2 from ribbon cable 1. After the ferrule is molded, then ribbon cable 1 is appropriately stripped and the individual fibers 2 are inserted into the fiber bores. Various techniques are used to fix the fibers in the molded ferrule and then the face 5 of the ferrule and the ends of the fibers 2 are polished.
As is known in the art, there is a premium placed on precise alignment of opposing optical fibers in a connector to minimize connection loss which diminished the qualify of the optical transmission through the connector. The issue of precisely aligning opposing optical fibers becomes even more sensitive with multi-fiber ferrules because of the need to precisely align all the optical fibers relative to each other and relative to the guide pin bores within the molded ferrule.
The prior art presently used a series of V-grooves machined into a block to retain bore forming pins extending through the mold cavity. FIG. 1 herein shows a cross-section of an example V-groove geometry where fiber bore forming pins 7 and guide bore forming pins 8 are shown disposed in V-grooves 9. The disadvantages of this or similar open groove constructions are many.
First, there is a tendency of the pins to float within the V-groove in the direction of arrow A during the molding process. This float contributes to imprecise alignment of the bores formed in the molded ferrule. Additionally, after repeated used of a mold cavity with the groove construction, flash begins to build up in areas indicated by B. This flash build up requires frequent cleaning of the V-grooves. Also, as can be seen, the pins contact the V-grooves along two lines of contact and thus all the friction forces of the repeated insertion and removal of the pins into the V-grooves are imparted along these two lines of contact thereby causing wear along the sides of the V-groove. This causes the alignment of the pins to become progressively more imprecise. Another disadvantage is that preciseness in the construction of the V-groove block in inherently limited. The V-grooves are machined into a stock piece without the ability to adjust the relationship of the grooves to each other.
Therefore a need exists for a guide block to retain the bore forming pins that reduces float of the pins during the molding process and improves wear resistance of the guide block. Additionally, a guide block is needed that eliminates the need to clean the guide block after each mold to remove flash. Additionally, a guide block is needed that allows the relationships between the bore forming pins to be continually adjusted during construction of the guide block to allow a more precise guide block to be constructed. Additionally, a need exists for a guide block that can be adjusted after it is constructed to account for gradual shifts in the bore pin relationships caused by repeated use of the guide.